The invention relates to an apparatus for use in the manufacture of semiconductors, and more particularly, to a method and an apparatus for reuse of an abrasive fluid used in the manufacture of semiconductor devices.
A chemical-mechanical polishing (CMP) device is used in flattening a wafer surface in a semiconductor manufacturing step. The CMP device employs an abrasive slurry, and accordingly, as the quantity of products manufactured increases, the quantity of used abrasive slurry also increases. The quantity of abrasive slurry used influences the manufacturing cost, and hence an efficient reuse of the used abrasive slurry or fluid is required.
In the conventional practice of flattening a wafer surface, an abrasive slurry in liquid form which comprises a commercially available abrasive stock having a weight percentage of approximately 25 wt % and diluted by deionized water to nearly 13 wt % is used. Used abrasive fluid is further diluted within the polishing device to produce an effluent which may have a concentration on the order of about 0.1 to 0.2 wt %, for example. It will be understood that the abrasive effluent contains fragments of films abraded from the wafer and impurities produced by a polishing table (or pad) of the polishing device. Abrasive effluents are generally passed through a neutralization treatment before disposal or delivered to an industrial waste disposal undertaker in the form of sludges which result from a drainage treatment. The abrasive fluid represents a significant proportion of the wafer processing cost, but the abrasive effluent has been disposed of without a reuse thereof.
Abrasive grains contained in the abrasive effluent are agglomerated to larger sizes. However, a single grain in the agglomeration has a grain diameter which remains substantially unchanged from the grain size which it exhibited before it was fed to the polishing step, and thus retains a grain size which is still useable in the abrasive operation. Nevertheless, the grain agglomerations are disposed of without being recycled.
The cost of disposing sludges delivered to the industrial waste disposal undertaker adds to the semiconductor manufacturing cost. Thus, reuse of the abrasive effluent is of importance in reducing the semiconductor manufacturing cost.
It is an object of the invention to provide a method and an apparatus which allow reuse of an abrasive effluent.